The statements in this section may serve as a background to help understand the invention and its application and uses, but may not constitute prior art.
Compared with conventional power devices made of silicon, Group III-Nitride (III-N) semiconductors possess a number of excellent electronic properties that enable the fabrication of modern power electronic devices and structures for use in a variety of applications. Silicon's limited critical electric field and relatively high resistance make currently available commercial power devices, circuits, and systems bulky, heavy, with further constraints on operating frequencies. On the other hand, higher critical electric field and higher electron density and mobility of III-N materials allow high-current, high-voltage, high-power and/or high-frequency performances of improved power transistors that are greatly desirable for advanced transportation systems, high-efficiency electricity generation and conversion systems, and energy delivery networks. Such systems rely on efficient converters to step-up or step-down electric voltages, and use power transistors capable of blocking large voltages and/or carrying large currents. For example, power transistors with blocking voltages of more than 500V are used in hybrid vehicles to convert DC power from the batteries to AC power. Some other exemplary applications of power transistors include power supplies, automotive electronics, automated factory equipment, motor controls, traction motor drives, high voltage direct current (HVDC) electronics, lamp ballasts, telecommunication circuits and display drives.
In spite of the enormous potential of III-N semiconductor devices for producing high-efficiency power electronics such as high power amplifiers and converters, a major factor that limit the performance and reliability of III-N high electron mobility transistors for high power and high frequency applications is high gate leakage current due to significant amount of surface defects and electron traps by surface or bulk trap states. In a conventional III-N transistor, a Schottky gate biased with a positive voltage during operation can have a gate leakage current as high as the drain current, leading to malfunction of the device. Gate leakage degradation at high electric fields are also commonly observed. Recently, gate leakage current and channel electric field management structures such as gate recesses, T-shaped and Γ-shaped gates, field-plates, and suitable passivation materials have been proposed and studied, some of which provide noticeable performance improvements. Nonetheless, further and significant reduction of gate leakage current are highly desirable for achieving high levels of reliability and stability under high-performance operations.
Therefore, in view of the aforementioned practicalities and difficulties, there is an unsolved need for Group III-Nitride semiconductor structures, and for reducing device failure mechanisms, preventing high gate leakage currents, increasing breakdown voltages, and generally improving the reliability and stability of semiconductor devices fabricated thereon.